Communication control device, program, and communication control method

ABSTRACT

There is provided a communication control device including an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device, and a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing. The decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

CROSS REFERENCE TO RELATED APPLICATION

The present continuation application claims the benefit of priorityunder U.S.C. §120 to U.S. application Ser. No. 14/430,126, filed on Mar.20, 2015, which was the National Stage of International Application No.PCT PCT/JP2013/076104, filed on Sep. 26, 2013, and claims the benefit ofpriority under 35 U.S.C. §119 from Japanese Application No. 2012-264137,filed on Dec. 3, 2012. The entire contnets of all of which are herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a communication control device, aprogram, and a communication control method.

BACKGROUND ART

Near field inter-terminal communication or device-to-devicecommunication (D2D communication) is a communication form in which asignal is directly transmitted between terminal devices, unlike acommunication form in which a signal passes through a base station incellular communication. Therefore, in the D2D communication, new useforms of terminal devices unlike the existing cellular communication areexpected to appear. For example, various applications such asinformation sharing by data communication between near terminal devicesor a group of near terminal devices, information distribution frominstalled terminal devices, and autonomous communication between devicescalled Machine to Machine (M2M) can be considered.

With regard to the significant increase in data traffic with the recentincrease of smartphones, the D2D communication can also be considered tobe utilized in off-loading of data. In recent years, for example,demands for transmission and reception of streaming data of movingimages have rapidly increased. However, since moving images generallyhave large data amounts, the moving images have a problem in that theyconsume many resources in a Radio Access Network (RAN). Accordingly,when terminal devices are in a state suitable for the D2D communicationsuch as a case in which a distance between terminal devices is small,resource consumption and process loads in the RAN can be suppressed byoff-loading moving image data in the D2D communication. Thus, the D2Dcommunication is useful for both communication providers and users.Therefore, at present, the D2D communication is recognized and noticedas one of the important technical areas necessary for Long TermEvolution (LTE) of the 3rd Generation Partnership Project (3GPP)standardization commission as well.

In the related art, as disclosed in the following patent literature,communication schemes such as Bluetooth (registered trademark) and WiFi(registered trademark) have been adopted in the D2D communication andcombinations of such communication schemes and communication schemes ofcellular communication such as Wideband Code Division Multiple Access(WCDMA) (registered trademark) and LTE have been combined as an example.

CITATION LIST Patent Literature

Patent Literature 1: JP 2010-279042A

SUMMARY OF INVENTION Technical Problem

However, when the same communication scheme as the communication scheme(for example, LTE) of the cellular communication is adopted in the D2Dcommunication and the cellular communication and the D2D communicationare not properly combined, transmission and reception of signals in theD2D communication may be obstructed. Specifically, for example, since adistance between terminal devices at the time of the D2D communicationis less than a distance between a base station and a terminal device,propagation delay in the D2D communication is less than propagationdelay in cellular communication. For this reason, when the terminaldevice does not transmit a signal of the D2D communication inconsideration of transmission and reception timings in cellularcommunication, there is a possibility of the signal of the D2Dcommunication not being properly received.

Accordingly, it is desirable to provide a structure capable of improvinga possibility of a signal being properly received in D2D communicationin which the same communication scheme as a communication scheme ofcellular communication is adopted.

Solution to Problem

According to the present disclosure, there is provided a communicationcontrol device including an acquisition unit configured to acquire areception timing at which a second radio communication device receives adownlink signal from a base station performing radio communication witha first radio communication device or the second radio communicationdevice, and a decision unit configured to decide a transmission timingat which the second radio communication device transmits a signal to thefirst radio communication device through inter-device communicationbased on the reception timing. The decided transmission timing is atiming later than a timing at which the second radio communicationdevice transmits an uplink signal.

According to the present disclosure, there is provided a program causinga computer to function as an acquisition unit configured to acquire areception timing at which a second radio communication device receives adownlink signal from a base station performing radio communication witha first radio communication device or the second radio communicationdevice, and a decision unit configured to decide a transmission timingat which the second radio communication device transmits a signal to thefirst radio communication device through inter-device communicationbased on the reception timing. The decided transmission timing is atiming later than a timing at which the second radio communicationdevice transmits an uplink signal.

According to the present disclosure, there is provided a communicationcontrol method including acquiring a reception timing at which a secondradio communication device receives a downlink signal from a basestation performing radio communication with a first radio communicationdevice or the second radio communication device, and deciding atransmission timing at which the second radio communication devicetransmits a signal to the first radio communication device throughinter-device communication based on the reception timing. The decidedtransmission timing is a timing later than a timing at which the secondradio communication device transmits an uplink signal.

Advantageous Effects of Invention

According to an embodiment of the present disclosure described above, itis possible to improve a possibility of a signal being properly receivedin D2D communication in which the same communication scheme as acommunication scheme of cellular communication is adopted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram illustrating an example of a radiocommunication system which is a premise of description of FIGS. 2 to 7.

FIG. 2 is an explanatory diagram illustrating a downlink signaltransmitted in radio communication according to LTE.

FIG. 3 is an explanatory diagram schematically illustrating an exampleof timings at which terminal devices receive downlink signals.

FIG. 4 is an explanatory diagram illustrating the details of the exampleof timings at which the terminal devices receive the downlink signals.

FIG. 5 is an explanatory diagram schematically illustrating an exampleof timings at which the terminal devices transmit uplink signals.

FIG. 6 is an explanatory diagram illustrating the details of an exampleof timings at which the terminal devices transmit the uplink signals.

FIG. 7 is an explanatory diagram illustrating timing advance.

FIG. 8 is an explanatory diagram illustrating a first example whentransmission and reception timings of signals in cellular communicationare applied to D2D communication.

FIG. 9 is an explanatory diagram illustrating a second example whentransmission and reception timings of signals in cellular communicationare applied to D2D communication.

FIG. 10 is an explanatory diagram illustrating an example of a schematicconfiguration of a radio communication system according to anembodiment.

FIG. 11 is a block diagram illustrating an example of the configurationof a terminal device according to an embodiment.

FIG. 12 is a first explanatory diagram illustrating a first example of aD2D transmission timing according to an embodiment.

FIG. 13 is a second explanatory diagram illustrating a first example ofa D2D transmission timing according to an embodiment.

FIG. 14 is a first explanatory diagram illustrating a second example ofa D2D transmission timing according to an embodiment.

FIG. 15 is a second explanatory diagram illustrating a second example ofa D2D transmission timing according to an embodiment.

FIG. 16 is a first explanatory diagram illustrating a third example of aD2D transmission timing according to an embodiment.

FIG. 17 is a second explanatory diagram illustrating a third example ofa D2D transmission timing according to an embodiment.

FIG. 18 is an explanatory diagram illustrating a first case in which aterminal device performs D2D communication with two or more otherterminal devices.

FIG. 19 is an explanatory diagram illustrating a second case in which aterminal device performs D2D communication with two or more otherterminal devices.

FIG. 20 is a sequence diagram illustrating an example of a schematicflow of a communication control process according to an embodiment.

FIG. 21 is an explanatory diagram illustrating a first example of cellswhen terminal devices performing the D2D communication are located indifferent cells.

FIG. 22 is an explanatory diagram illustrating a second example of cellswhen terminal devices performing the D2D communication are located indifferent cells.

FIG. 23 is a sequence diagram illustrating a first example of aschematic flow of a communication control process according to amodification example of an embodiment.

FIG. 24 is a sequence diagram illustrating a second example of aschematic flow of a communication control process according to amodification example of an embodiment.

FIG. 25 is a block diagram illustrating an example of a schematicconfiguration of a smartphone to which technology according of thepresent disclosure may be applied.

FIG. 26 is a block diagram illustrating an example of a schematicconfiguration of a car navigation device to which technology accordingto the present disclosure may be applied.

FIG. 27 is a block diagram illustrating a first example of a schematicconfiguration of an eNB to which the technology of the presentdisclosure is applied.

FIG. 28 is a block diagram illustrating a second example of a schematicconfiguration of an eNB to which the technology of the presentdisclosure is applied.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

The description will be made in the following order.

1. Introduction

1.1. Transmission and reception timings of signals in cellularcommunication scheme

1.2. Technical problem in D2D communication

2. Schematic configuration of radio communication system

3. Configuration of terminal device

4. Flow of process

5. Modification examples

6. Introduction

6.1. Application to terminal device

6.2. Application to base station

7. Conclusion

1. INTRODUCTION

First, transmission and reception timings of signals in a cellularcommunication scheme and a technical problem in D2D communication willbe described with reference to FIGS. 1 to 9.

<1.1. Transmission and Reception Timings of Signals in CellularCommunication Scheme>

Transmission and reception timings of signals in a cellularcommunication scheme will be described with reference to FIGS. 1 to 7.Here, the timings of the transmission and reception of the signals in,for example, LTE will be described.

(Configuration of Radio Communication System)

FIG. 1 is an explanatory diagram illustrating an example of a radiocommunication system which is a premise of description of FIGS. 2 to 7.Terminal devices 10 and a base station 20 are illustrated in FIG. 1. Theterminal device 10 is referred to user equipment (UE) and the basestation 20 is referred to as an evolved node B (eNB). A cell 21 formedby the base station 20 is also illustrated. In such a radiocommunication system, radio communication is performed as cellularcommunication between each terminal device 10 and the base station 20.Radio communication is performed as D2D communication between theterminal devices 10. For example, the terminal devices 10A and 10Bperform the D2D communication.

In this example, the terminal device 10A is located to be more distantthan the terminal device 10B from the base station 20. That is, adistance between the terminal device 10A and the base station 20 islonger than a distance between the terminal device 10B and the basestation 20.

(Signal in LTE) Downlink

In LTE, Orthogonal Frequency Division Multiplexing (OFDM) is adopted ina downlink. Fourteen OFDM symbols are transmitted for each of thesubframes which are units of times of radio communication. Hereinafter,a specific example of this point will be described with reference toFIG. 2.

FIG. 2 is an explanatory diagram illustrating a downlink signaltransmitted in radio communication according to LTE. A downlink signaltransmitted with one subframe in radio communication according to LTE isillustrated in FIG. 2. In LTE, fourteen OFDM symbols are generallyincluded in one subframe. In other words, one subframe includes twoslots and one slot includes seven OFDM symbols. Each OFDM symbolincludes a cyclic prefix (CP) in its beginning.

The CP is a guard interval for removing inter-symbol interference inwhich a delay wave of the OFDM symbol has an influence on the subsequentOFDM symbol. The CP is generated, for example, by copying signalcorresponding to a predetermined time of the last end of the OFDMsymbol. A terminal device receiving the OFDM symbol neglects the signalof the CP in the OFDM symbol and demodulates the remaining signals ofthe OFDM symbol. The cyclic prefix contributes to removal ofinter-subcarrier interference.

In the case of a normal cyclic prefix, the length of the OFDM symbol isabout 66.67 microseconds. The length of the cyclic prefix included inthe beginning of each symbol is about 4.687 microseconds.

Uplink

In LTE, on the other hand, a Single Carrier Frequency Division MultipleAccess (SC-FDMA) is adopted in an uplink. The SC-FDMA symbol istransmitted in a time direction. The SC-FDMA symbol also includes a CPas in the OFDM symbol.

(Transmission and Reception Timings of Signals) Downlink

In a downlink of LTE, the base station 20 transmits a downlink signalsimultaneously at a certain frame timing. That is, the base station 20transmits the downlink signal to each terminal device 10 at the sametiming. This is because resource blocks for transmitting data destinedfor the terminal devices 10 are subjected to signal processing inparallel at the same frame timing and the resource blocks aretransmitted simultaneously from an antenna after amplification in thebase station 20.

On the other hand, the terminal device 10 receives a downlink signalafter propagation delay according to a distance between the terminaldevice 10 and the base station 20 rather than the frame timing. Aspecific example of this point will be described with reference to FIGS.3 and 4.

FIG. 3 is an explanatory diagram schematically illustrating an exampleof timings at which terminal devices receive the downlink signals.Timings at which the base station 20 transmits downlink signals to theterminal devices 10A and 10B with the subframes are illustrated in FIG.3. Thus, the base station 20 transmits the downlink signalssimultaneously at a certain frame timing. Further, timings at which theterminal devices 10A and 10B receive the downlink signals are alsoillustrated in FIG. 3. Thus, the terminal devices 10A and 10B startreceiving the downlink signal later than the frame timing.

FIG. 4 is an explanatory diagram illustrating the details of an exampleof timings at which the terminal devices receive the downlink signals.The timings at which the terminal devices 10A and 10B illustrated inFIG. 3 receive the downlink signals are illustrated in more detail inFIG. 4. In this example, as illustrated in FIG. 1, the terminal device10A is more distant from the base station 20 than the terminal device10B. Therefore, propagation delay PD (B→T_(A)) in a path from the basestation 20 to the terminal device 10A is greater than propagation delayPD (B→T_(B)) in a path from the base station 20 to the terminal device10B. That is, “PD (B→T_(A))>PD (B→T_(B))” is satisfied. Accordingly, atiming at which the terminal device 10A starts receiving the downlinksignal is later than a timing at which the terminal device 10B startsreceiving the downlink signal. Thus, the reception timing of thedownlink signal of the terminal device 10 is decided depending on wherethe terminal device 10 is located within the cell 21.

Uplink

In an uplink of LTE, the base station 20 receives uplink signalssimultaneously at a given frame timing. That is, the base station 20receives the uplink signals from the respective terminal devices 10 atthe same timing.

On the other hand, the terminal device 10 starts transmitting the uplinksignal earlier than the frame timing rather than the frame timing inconsideration of the propagation delay according to the distance betweenthe terminal device 10 and the base station 20. A specific example ofthis point will be described with reference to FIGS. 5 and 6.

FIG. 5 is an explanatory diagram schematically illustrating an exampleof timings at which the terminal devices transmit the uplink signals.The timings at which the base station 20 receive the uplink signals fromthe terminal devices 10A and 10B with the subframes are illustrated inFIG. 5. Thus, the base station 20 receives the uplink signalssimultaneously at a certain frame timing. The timings at which theterminal devices 10A and 10B transmit the uplink signals are alsoillustrated in FIG. 5. Thus, the terminal devices 10A and 10B starttransmitting the uplink signals earlier than the frame timing.

FIG. 6 is an explanatory diagram illustrating the details of an exampleof timings at which the terminal devices transmit the uplink signals.The timings at which the terminal devices 10A and 10B illustrated inFIG. 5 receive the uplink signals are illustrated in more detail in FIG.6. In this example, as illustrated in FIG. 1, the terminal device 10A ismore distant from the base station 20 than the terminal device 10B.Therefore, propagation delay PD (T_(A)→B) in a path from the terminaldevice 10A to the base station 20 is greater than propagation delay PD(T_(B)→B) in a path from the terminal device 10B to the base station 20.That is, “PD (T_(A)→B)>PD (T_(B)→B)” is satisfied. Accordingly, a timingat which the terminal device 10A starts transmitting the uplink signalis earlier than a timing at which the terminal device 10B startstransmitting the uplink signal. Thus, the transmission timing of theuplink signal of the terminal device 10 is decided depending on wherethe terminal device 10 is located within the cell 21.

Thus, a technology for enabling the terminal devices 10 to transmit theuplink signals so that the uplink signals from the respective terminaldevices 10 simultaneously reach the base station 20 is referred to astiming advance (TA). Hereinafter, the more detailed content of thispoint will be described with reference to FIG. 7.

FIG. 7 is an explanatory diagram illustrating the timing advance. Atransmission timing of the uplink signal of the terminal device 10A anda transmission timing of the downlink signal of the terminal device 10Aare illustrated in FIG. 7. Thus, the transmission timing of the uplinksignal is earlier than the frame timing by the same time as thepropagation delay PD (T_(A)→B). The reception timing of the downlinksignal is later than the frame timing by the propagation delay PD(B→T_(A)). In general, the propagation delay PD (T_(A)→B) is the same asthe propagation delay PD (B→T_(A)). That is, “PD (T_(A)→B)=PD (B→T_(A))”is satisfied. Accordingly, the terminal device 100A transmits the uplinksignal earlier than a timing at which the downlink signal is to bereceived by a time twice the propagation delay PD (B→T_(A)) (or thepropagation delay PD (T_(A)→B)).

The terminal device 10 knows the timing at which the downlink signal isto be received since the terminal device 10 receives the downlinksignal. The terminal device 10 receives a timing advance value (TAvalue) as information used to decide a timing at which the uplink signalis transmitted from the base station. For example, the terminal device10 is notified of an initial value of the TA value with a random accessresponse at the time of random access. The terminal device 10 decides atiming earlier than the timing at which the downlink signal istransmitted by a time corresponding to the TA value as a timing at whichthe uplink signal is transmitted. That is, the time corresponding to theTA value corresponds to a time generally twice the propagation delaybetween the terminal device 10 and the base station. For example, a TAvalue corresponding to a longer time than the terminal device 10 locatednearer the center of the cell is given to the terminal device 10 locatedin a cell edge of the cell 21. The TA value in LTE is an 11-bit valuefrom 0 to 1282. A pitch width of the TA value for adjusting thetransmission timing is about 0.52 microseconds. Accordingly, thetransmission timing of the terminal device 10 can be adjusted up to 0.67milliseconds.

<1.2. Technical Problem>

As described above, signals are transmitted and received in the cellularcommunication. On the other hand, it is not preferable to apply thetransmission and reception timings of the signals in the cellularcommunication directly to the D2D communication between the terminaldevices 10. Hereinafter, a specific example of this point will bedescribed with reference to FIGS. 8 and 9. In this example, the OFDM isadopted in the D2D communication.

FIG. 8 is an explanatory diagram illustrating a first example when thetransmission and reception timings of signals in the cellularcommunication are applied to the D2D communication. In the example ofFIG. 8, the terminal device 10B is a transmission side device of the D2Dcommunication and the terminal device 10A is a reception side device ofthe D2D communication. A transmission timing at which the base station20 transmits a downlink signal and a reception timing at which theterminal device 10A receives the downlink signal are illustrated in FIG.8. These timings have been described with reference to FIG. 4.

A transmission timing at which the terminal device 10B transmits a D2Dcommunication signal through the D2D communication and a receptiontiming at which the terminal device 10A actually receives the D2Dcommunication signal are also illustrated in FIG. 8. In this example,since the transmission and reception timings in the cellularcommunication are directly applied, the transmission timing at which theterminal device 10B transmits the D2D communication signal is the sameas the transmission timing at which the terminal device 10B transmitsthe uplink signal. A reception timing at which the terminal device 10Aactually receives the D2D communication signal is later than thetransmission timing at which the terminal device 10B transmits the D2Dcommunication signal by propagation delay PD (T_(A)→T_(B)). Since thedistance between the terminal devices 10A and 10B is small at the timeof the D2D communication, the propagation delay PD (T_(A)→T_(B)) becomesvery small.

As a result, as illustrated in FIG. 8, a large deviation may occurbetween a reception timing at which the terminal device 10A receives thedownlink signal and a reception timing at which the terminal device 10Aactually receives the D2D communication signal. When the terminal device10A demodulates a signal after the reception timing at which theterminal device 10A receives the downlink signal, a part of the D2Dcommunication signal is not demodulated. The part includes not only theCP but also a signal other than the CP. Accordingly, the signal is notproperly received.

FIG. 9 is an explanatory diagram illustrating a second example when thetransmission and reception timings of signals in the cellularcommunication are applied to the D2D communication. In the example ofFIG. 9, the terminal device 10A is a transmission side device of the D2Dcommunication and the terminal device 10B is a reception side device ofthe D2D communication. A transmission timing at which the base station20 transmits a downlink signal and a reception timing at which theterminal device 10B receives the downlink signal are illustrated in FIG.9. These timings have been described with reference to FIG. 4.

A transmission timing at which the terminal device 10A transmits a D2Dcommunication signal in the D2D communication and a reception timing atwhich the terminal device 10B actually receives the D2D communicationsignal are also illustrated in FIG. 9. In this example, since thetransmission and reception timings in the cellular communication aredirectly applied, the transmission timing at which the terminal device10A transmits the D2D communication signal is the same as thetransmission timing at which the terminal device 10A transmits theuplink signal. A reception timing at which the terminal device 10Bactually receives the D2D communication signal is later than thetransmission timing at which the terminal device 10A transmits the D2Dcommunication signal by propagation delay PD (T_(B)→T_(A)). Since thedistance between the terminal devices 10A and 10B is not distant at thetime of the D2D communication, the propagation delay PD (T_(B)→T_(A))becomes very small.

As a result, as illustrated in FIG. 9, a large deviation may occurbetween a reception timing at which the terminal device 10B receives thedownlink signal and a reception timing at which the terminal device 10Bactually receives the D2D communication signal. When the terminal device10A demodulates signals after the reception timing at which the terminaldevice 10B receives the downlink signal, some of the D2D communicationsignals are not demodulated. Some of the signals include not only the CPbut also a signal other than the CP. Accordingly, the signal is notproperly received.

As described above with reference to FIGS. 8 and 9, when an adjustmentwidth (that is, a time corresponding to the TA value) of an uplinktransmission timing by the TA is large, a portion other than the CP ofthe D2D communication signal is not demodulated and the D2Dcommunication signal is not properly received. Since the D2Dcommunication is assumed to be frequency used mainly in a cell edgedistant from the base station 20, the TA value in regard to the terminaldevice 10 performing the D2D communication is assumed to be a relativelylarge value. Accordingly, there is a possibility of the D2Dcommunication signal not being properly demodulated.

The above-mentioned problem will be described using more detailednumerical values. For example, the terminal devices 10A and 10B areassumed to be present in a cell edge of a cell with a radius of 1kilometer. In this case, propagation delay in a path from the basestation 20 to the terminal device 10 is about 3.33 microseconds.Accordingly, when the distance between the terminal devices 10 isneglected, deviation of a reception timing between the terminal devices10 is about 6.66 microseconds. On the other hand, the length of the CPis 4.687 microseconds. Accordingly, when the deviation of the receptiontiming exceeds the length of the CP, the D2D communication signals arenot properly received.

In the above-described example, the distance between the terminal device10 and the base station 20 is 1 kilometer. However, when this distanceis shorter, the D2D communication signals can be properly received. Forexample, when the distance between the terminal device 10 and the basestation 20 is 700 meters, the propagation delay is 2.33 microseconds. Inthis case, the deviation of the reception timing is about 4.66microseconds. Accordingly, the propagation delay permitted in the D2Dcommunication is 0.021 microseconds in consideration of the fact thatthe cyclic prefix has a length of 4.687 microseconds. This propagationdelay corresponds to a distance of 6.3 meters. However, under theconstraint of the propagation delay or the distance, a large influenceon the D2D communication can occur due to, for example, a slight changein the propagation delay caused by movement of the terminal device 10 ora change in a propagation path. Accordingly, reliable communication isconsidered not to be ensured.

Thus, when the transmission and reception timings optimized for thecommunication with the base station 20 are used in the terminal device10, whether the D2D communication is possible depends on the distancebetween the terminal device 10 and the base station 20 and the distancebetween the terminal devices 10 performing the D2D communication. Thatis, large constraint may be imposed on the D2D communication.

Accordingly, in the embodiment, a possibility of signals being properlyreceived in the D2D communication in which the same communication schemeas the communication scheme of the cellular communication is adopted canbe configured to be improved. More specifically, it is possible toloosen or remove the constraints in the D2D communication, such as thedistance between the base station 20 and the terminal devices 10performing the D2D communication, the distance between the terminaldevices 10 performing the D2D communication, and the like.

2. SCHEMATIC CONFIGURATION OF RADIO COMMUNICATION SYSTEM

Next, a schematic configuration of the radio communication system 1according to an embodiment of the present disclosure will be describedwith reference to FIG. 10. FIG. 10 is an explanatory diagramillustrating an example of the schematic configuration of the radiocommunication system 1 according to the embodiment. Referring to FIG.10, the radio communication system 1 includes terminal devices 100 and abase station 200. The radio communication system 1 adopts, for example,LTE as a communication scheme of the cellular communication.

The terminal device 100 performs radio communication with the basestation 200 when the terminal device 100 is located within a cell 21formed by the base station 200. That is, the terminal device 100receives a downlink signal transmitted by the base station 200 andtransmits an uplink signal to the base station 200. For example, theterminal device 100 receives the downlink signal according to the OFDMand transmits an uplink signal according to the SC-FDMA.

The terminal device 100 performs D2D communication with another terminaldevice 100. For example, the terminal device 100 transmits a signalthrough the D2D communication according to a predetermined radiocommunication scheme and receives a signal according to thepredetermined radio communication scheme. The predetermined radiocommunication scheme is, for example, a radio communication scheme usedby the base station 200 to transmit a downlink signal. That is, thepredetermined radio communication scheme is the OFDM. That is, theterminal device 100 transmits and receives signals according to the OFDMthrough the D2D communication.

The base station 200 performs the radio communication with the terminaldevice 100 located within the cell 21. That is, the base station 200transmits a downlink signal to the terminal device 100 and receives anuplink signal from the terminal device 100. For example, the basestation 200 transmits a downlink signal according to the OFDM andreceives an uplink signal according to the SC-FDMA.

3. CONFIGURATION OF TERMINAL DEVICE

An example of the configuration of the terminal device 100 according tothe embodiment will be described with reference to FIGS. 11 to 19. FIG.11 is a block diagram illustrating an example of the configuration ofthe terminal device 100 according to the embodiment. Referring to FIG.11, the terminal device 100 includes an antenna unit 110, a radiocommunication unit 120, a storage unit 130, and a control unit 140.

(Antenna Unit 110)

The antenna unit 110 receives the radio signal and outputs the receivedradio signal to the radio communication unit 120. The antenna unit 110transmits a transmission signal output by the radio communication unit120.

(Radio Communication Unit 120)

The radio communication unit 120 performs the radio communication withanother device. For example, when the terminal device 100 is locatedwithin the cell 21 formed by the base station 200, the radiocommunication unit 120 performs the radio communication with the basestation 200. That is, the radio communication unit 120 receives thedownlink signal transmitted by the base station 200 and transmits theuplink signal to the base station 200. For example, the radiocommunication unit 120 receives the downlink signal according to theOFDM and transmits the uplink signal according to the SC-FDMA.

In particular, in the embodiment, the radio communication unit 120performs the D2D communication with another terminal device 100. Forexample, the radio communication unit 120 transmits a signal accordingto a predetermined radio communication scheme through the D2Dcommunication and receives a signal according to the predetermined radiocommunication scheme. The predetermined radio communication scheme is,for example, a radio communication scheme used by the base station 200to transmit the downlink signal. That is, the predetermined radiocommunication scheme is the OFDM. The radio communication unit 120transmits and receives the signals according to the OFDM through the D2Dcommunication.

(Storage Unit 130)

The storage unit 130 stores a program and data for an operation of theterminal device 100.

(Control Unit 140)

The control unit 140 supplies various functions of the terminal device100. The control unit 140 includes an information acquisition unit 141and a transmission timing decision unit 143.

(Information Acquisition Unit 141)

The information acquisition unit 141 acquires a reception timing(hereinafter referred to as a “downlink reception timing”) at which theterminal device 100 (the radio communication unit 120) receives thedownlink signal from the base station 200 performs radio communicationwith the terminal device 100 or the other terminal device 100. Forexample, the terminal device 100 and the other terminal device 100 arelocated within the same cell 21 and the base station 200 is a basestation of the cell 21. That is, the terminal device 100 and the otherterminal device 100 receive downlink signals from the same base station200. Then, the information acquisition unit 141 acquires the downlinkreception timing at which the terminal device 100 (the radiocommunication unit 120) receives the downlink signal from the basestation 200. For example, the information acquisition unit 141 acquiresthe downlink reception timing from a detection result of the downlinksignal by the radio communication unit 120.

For example, the information acquisition unit 141 further acquirestiming advance information (TA information) to decide a timing(hereafter referred to as an uplink transmission timing) at which theterminal device 100 (the radio communication unit 120) transmits theuplink signal. The TA information is, for example, a TA value. Asdescribed above, since the terminal device 100 is notified of the TAvalue with a random access response at the time of random access, theinformation acquisition unit 141 acquires the TA value notified of withthe random access response via the radio communication unit 120.

The information acquisition unit 141 may further acquire the TAinformation to decide a timing (that is, an uplink transmission timingof the other terminal device 100) at which the other terminal device 100transmits the uplink signal. In this case, for example, the base station200 may acquire the TA value of the other terminal device 100 andtransmit the TA value to the terminal device 100. When the radiocommunication unit 120 receives the TA value of the other terminaldevice 100, the information acquisition unit 141 may acquire the TAvalue of the other terminal device 100.

(Transmission Timing Decision Unit 143)

The transmission timing decision unit 143 decides the transmissiontiming at which the terminal device 100 transmits a signal.

For example, the transmission timing decision unit 143 decides atransmission timing (hereinafter referred to as an “uplink transmissiontiming”) at which the terminal device 100 (the radio communication unit120) transmits the uplink signal to the base station 200. Morespecifically, for example, the transmission timing decision unit 143decides a timing earlier than the downlink reception timing by a timecorresponding to the acquired TA value as the uplink transmissiontiming. Then, the transmission timing decision unit 143 causes the radiocommunication unit 120 to transmit the uplink signal at the decideduplink transmission timing.

In particular, in the embodiment, the transmission timing decision unit143 decides a transmission timing (hereinafter referred to as a “D2Dtransmission timing”) at which the terminal device 100 (the radiocommunication unit 120) transmits a signal to the other terminal device100 through the D2D communication based on the acquired downlinkreception timing. The decided D2D transmission timing is a timing laterthan a timing (that is, the uplink transmission timing) at which theterminal device 100 (the radio communication unit 120) transmits theuplink signal.

As described above, when the D2D transmission timing of a transmissionside device of the D2D communication is the same as the uplinktransmission timing, the D2D communication signal may arrive at areception side device quite earlier than the downlink reception timingof the reception side device of the D2D communication. For this reason,there is a possibility of a portion other than the CP in the D2Dcommunication signal not being demodulated according to distancesbetween the base station 200, and the reception side device and thetransmission side device and the distance between the reception sidedevice and the transmission side device.

On the other hand, in the embodiment, when the D2D transmission timingis a timing later than the uplink transmission timing, the downlinkreception timing and the D2D reception timing of a partner side arecloser. Accordingly, there is a high possibility of the D2Dcommunication signal being properly received. In other words, it ispossible to loosen constraints (for example, the distances between thebase station 200, and the reception side device and the transmissionside device and the distance between the reception side device and thetransmission side device) for proper reception of the D2D communicationsignal. As a result, off-loading can be performed more effectively,which considerably contributes to an increase a system capacity.

Hereinafter, a more specific example of the decided D2D transmissiontiming will be described.

First Example of D2D Transmission Timing

As a first example, the transmission timing decision unit 143 decidesthe D2D transmission timing based on the downlink reception timing ofthe terminal device 100 and the TA information of the terminal device100. As described above, the TA information is, for example, a TA value.Since the TA information (for example, a TA value) is an existingparameter of which the terminal device 100 is notified at the time ofthe random access, it is not necessary for the base station 200 totransmit a new control signal.

For example, the decided D2D transmission timing is a timing earlierthan the downlink reception timing. For example, the transmission timingdecision unit 143 multiples a time corresponding to the TA value of theterminal device 100 by a coefficient P (where 0<P<1). Then, thetransmission timing decision unit 143 decides the timing earlier thanthe downlink reception timing by a time of the multiplication result asthe D2D transmission timing. Then, the transmission timing decision unit143 causes the radio communication unit 120 to transmit the D2Dcommunication signal at the decided D2D transmission timing.

In this way, it is possible to prevent a period in which the partnerdevice actually receives the D2D communication signal from not enteringa period in which the partner device receives the downlink signalbecause the D2D transmission timing is too late.

For example, the decided D2D transmission timing is a timing later thana timing (hereinafter referred to as a “downlink transmission timing”)at which the base station 200 transmits the downlink signal. Forexample, the downlink transmission timing is a timing earlier than thedownlink reception timing by half of the time corresponding to the TAinformation of the terminal device 100.

Specifically, for example, the transmission timing decision unit 143multiples a time corresponding to the TA value of the terminal device100 by the coefficient P (where 0<P≦1/2). Then, the transmission timingdecision unit 143 decides a timing earlier than the downlink receptiontiming by a time of the multiplication result as the D2D transmissiontiming.

In this way, the D2D transmission timing is later than the downlinktransmission timing of the base station. Since the downlink receptiontiming of the partner device is at least later than the downlinktransmission timing, the downlink reception timing and the D2Dtransmission timing are closer. Accordingly, there is a high possibilityof the D2D communication signal being properly received. In other words,it is possible to loosen constraints (for example, the distances betweenthe base station 200, and the reception side device and the transmissionside device and the distance between the reception side device and thetransmission side device) for proper reception of the D2D communicationsignal.

As a specific example, the decided D2D transmission timing is a timing(that is, the downlink transmission timing) at which the base station200 transmits the downlink signal. As described above, for example, thedownlink transmission timing is a timing earlier than the downlinkreception timing by half of the time corresponding to the TA informationof the terminal device 100. For example, the transmission timingdecision unit 143 multiples the time corresponding to the TA value ofthe terminal device 100 by a coefficient ½. Then, the transmissiontiming decision unit 143 decides the timing earlier than the downlinkreception timing by the time of the multiplication result as the D2Dtransmission timing.

In this way, the D2D transmission timing becomes nearly constant betweenthe terminal devices 100. That is, a variation in the D2D transmissiontiming by the terminal device 100 is small irrespective of the positionof each terminal device 100 within the cell 21, a frequency band usedfor the D2D communication, and a duplex communication scheme (forexample, an FDD scheme or a TDD scheme).

Hereinafter, a specific example will be described with reference toFIGS. 12 and 13.

FIG. 12 is a first explanatory diagram illustrating a first example of aD2D transmission timing according to the embodiment. In the example ofFIG. 12, the terminal device 100B is a transmission side device of theD2D communication and the terminal device 100A is a reception sidedevice of the D2D communication. A downlink transmission timing at whichthe base station 200 transmits a downlink signal and a downlinkreception timing at which the terminal device 100A receives the downlinksignal are illustrated in FIG. 12. This point is the same as that of theexample illustrated in FIG. 8.

A D2D transmission timing at which the terminal device 100B transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100A actually receives the D2Dcommunication signal are also illustrated in FIG. 12. In this example,the D2D transmission timing of the terminal device 100B is almost thesame as the downlink transmission timing of the base station 200. As aresult, a deviation between the reception timings (that is, a deviationbetween the D2D reception timing and the downlink reception timing inthe terminal device 100A) illustrated in FIG. 12 is less than thedeviation between the reception timings illustrated in FIG. 8. As aresult, the deviation between the reception timings is less than thelength of the CP and the terminal device 100A can properly receive theD2D communication signal.

FIG. 13 is a second explanatory diagram illustrating the first exampleof the D2D transmission timing according to the embodiment. In theexample of FIG. 13, the terminal device 100A is a transmission sidedevice of the D2D communication and the terminal device 100B is areception side device of the D2D communication. A downlink transmissiontiming at which the base station 200 transmits a downlink signal and adownlink reception timing at which the terminal device 100B receives thedownlink signal are illustrated in FIG. 13. This point is the same asthat of the example illustrated in FIG. 9.

A D2D transmission timing at which the terminal device 100A transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100B actually receives the D2Dcommunication signal are also illustrated in FIG. 13. In this example,the D2D transmission timing of the terminal device 100A is almost thesame as the downlink transmission timing of the base station 200. As aresult, a deviation between the reception timings (that is, a deviationbetween the D2D reception timing and the downlink reception timing inthe terminal device 100B) illustrated in FIG. 12 is less than thedeviation between the reception timings illustrated in FIG. 9. As aresult, the deviation between the reception timings is less than thelength of the CP and the terminal device 100B can properly receive theD2D communication signal.

Second Example of D2D Transmission Timing

As a second example, a decided D2D transmission timing is a receptiontiming (that is, a downlink reception timing) at which the terminaldevice 100 receives the downlink signal. That is, the transmissiontiming decision unit 143 decides the acquired downlink reception timingas the D2D transmission timing. Then, the transmission timing decisionunit 143 causes the radio communication unit 120 to transmit the D2Dcommunication signal at the decided D2D transmission timing.

In general, the terminal devices 100 (for example, the terminals 100Aand 100B) performing the D2D communication are located nearby. That is,the distance between the terminal devices 100 is small. Therefore, adifference between the downlink reception timing of the transmissionside device and the downlink reception timing of the reception side inthe D2D communication is small. Further, in the D2D communication,propagation delay from the transmission side device to the receptionside device is small. Accordingly, when the transmission side device(for example, the terminal device 100A) of the D2D communicationtransmits a D2D communication signal at a downlink reception timing ofthe own device, the reception side device (for example, the terminaldevice 100B) can receive the D2D communication signal at a timing closeto the downlink reception timing of the own device. Accordingly, thereis a high possibility of the D2D communication signal being properlyreceived. In other words, it is possible to loosen constraints (forexample, the distances between the base station 200, and the receptionside device and the transmission side device and the distance betweenthe reception side device and the transmission side device) for properreception of the D2D communication signal.

In this case, information other than the reception timing is notnecessary. Accordingly, even when the TA value is not yet acquired (forexample, the terminal device 100 does not perform random access and isin an idle state), the terminal device 100 can transmit the D2Dcommunication signal at a proper D2D transmission timing.

Hereinafter, a specific example will be described with reference toFIGS. 14 and 15.

FIG. 14 is a first explanatory diagram illustrating a second example ofthe D2D transmission timing according to the embodiment. In the exampleof FIG. 14, the terminal device 100B is a transmission side device ofthe D2D communication and the terminal device 100A is a reception sidedevice of the D2D communication. A downlink transmission timing at whichthe base station 200 transmits a downlink signal and a downlinkreception timing at which the terminal device 100A receives the downlinksignal are illustrated in FIG. 14. This point is the same as those ofthe examples illustrated in FIGS. 8 and 12.

A D2D transmission timing at which the terminal device 100B transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100A actually receives the D2Dcommunication signal are also illustrated in FIG. 14. In this example,the D2D transmission timing of the terminal device 100B is the same asthe downlink reception timing of the terminal device 100B. As a result,a deviation between the reception timings (that is, a deviation betweenthe D2D reception timing and the downlink reception timing in theterminal device 100A) illustrated in FIG. 14 is less than the deviationbetween the reception timings illustrated in FIG. 8. As a result, thedeviation between the reception timings is less than the length of theCP and the terminal device 100A can properly receive the D2Dcommunication signal.

FIG. 15 is a second explanatory diagram illustrating the second exampleof the D2D transmission timing according to the embodiment. In theexample of FIG. 15, the terminal device 100A is a transmission sidedevice of the D2D communication and the terminal device 100B is areception side device of the D2D communication. A downlink transmissiontiming at which the base station 200 transmits a downlink signal and adownlink reception timing at which the terminal device 100B receives thedownlink signal are illustrated in FIG. 15. This point is the same asthat of the example illustrated in FIG. 9.

A D2D transmission timing at which the terminal device 100A transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100B actually receives the D2Dcommunication signal are also illustrated in FIG. 15. In this example,the D2D transmission timing of the terminal device 100A is the same asthe downlink reception timing of the terminal device 100A. As a result,a deviation between the reception timings (that is, a deviation betweenthe D2D reception timing and the downlink reception timing in theterminal device 100B) illustrated in FIG. 15 is less than the deviationbetween the reception timings illustrated in FIG. 9. In this example,the D2D reception timing is slightly later than the downlink receptiontiming. Accordingly, when a reception period of the downlink signal isset to be slightly longer than the length of the OFDM symbol, theterminal device 100B can properly receive the D2D communication signal.

The above-described D2D transmission timing may be applied to a case inwhich a predetermined condition is satisfied. For example, when a timeadvance group (TAG) of the transmission side device (for example, theterminal device 100A) is the same as a TAG of the reception side device(for example, the terminal device 100B), the above-described D2Dtransmission timing may be applied.

The fact that the TAG of the transmission side device is the same as theTAG of the reception side device means that the TA value of thetransmission side device is the same as the TA value of the receptionside device. Accordingly, when the TAG of the transmission side deviceis the same as the TAG of the reception side device, the downlinkreception timing of the transmission side device is the same as thedownlink reception timing of the reception side device. Accordingly, thedownlink reception timing and the D2D reception timing in the receptionside device can be closer.

When the TAGs of two terminal devices performing the D2D communicationare not the same, the D2D transmission timings may be individuallyadjusted by an offset value of the transmission timing.

Such determination of whether the TAGs are the same and adjustment ofthe transmission timings by the offset value are performed by the basestation 200. Then, for example, the base station 200 notifies theterminal device 100 performing the D2D communication.

Third Example of D2D Transmission Timing

As a third example, the transmission timing decision unit 143 decidesthe D2D transmission timing based on the downlink reception timing ofthe terminal device 100, the TA information of the terminal device 100,and the TA information of another terminal device 100.

For example, the decided D2D transmission timing is a timing (that is, adownlink reception timing of the other terminal device 100) at which theother terminal device 100 (that is, a reception side terminal device ofthe D2D communication) receives a downlink signal from the base station200. For example, the downlink reception timing of the other terminaldevice 100 is a timing later than a timing (that is, a downlinktransmission timing) at which the base station 200 transmits thedownlink signal by half of a time corresponding to the TA information ofthe other terminal device 100.

Specifically, for example, the transmission timing decision unit 143multiples the time corresponding to the TA value of the terminal device100 by a coefficient ½. Then, the transmission timing decision unit 143calculates a timing earlier than the downlink transmission timing by atime of a multiplication result as the downlink transmission timing ofthe base station 200. The transmission timing decision unit 143calculates a timing later than the calculated downlink transmissiontiming by half of a time corresponding to the TA information of theother terminal device 100 as the downlink reception timing of the otherterminal device 100. The half time corresponds to propagation delay fromthe base station 200 to the other terminal device 100. The transmissiontiming decision unit 143 decides the downlink reception timing of theother terminal device 100 as a D2D transmission timing of the terminaldevice 100. The transmission timing decision unit 143 causes the radiocommunication unit 120 to transmit the D2D communication signal at thedecided D2D transmission timing.

In general, the terminal devices 100 (for example, the terminals 100Aand 100B) performing the D2D communication are located nearby. That is,the distance between the terminal devices 100 is small. Therefore, inthe D2D communication, propagation delay from the transmission sidedevice to the reception side device is small. Accordingly, when thetransmission side device (for example, the terminal device 100A) of theD2D communication transmits a D2D communication signal at a downlinkreception timing of the reception side device (for example, the terminaldevice 100B), the reception side device can receive the D2Dcommunication signal at a timing close to the downlink reception timingof the own device. Accordingly, there is a high possibility of the D2Dcommunication signal being properly received. In other words, it ispossible to loosen constraints (for example, the distances between thebase station 200, and the reception side device and the transmissionside device and the distance between the reception side device and thetransmission side device) for proper reception of the D2D communicationsignal.

Hereinafter, a specific example will be described with reference toFIGS. 16 and 17.

FIG. 16 is a first explanatory diagram illustrating a third example ofthe D2D transmission timing according to the embodiment. In the exampleof FIG. 16, the terminal device 100B is a transmission side device ofthe D2D communication and the terminal device 100A is a reception sidedevice of the D2D communication. A downlink transmission timing at whichthe base station 200 transmits a downlink signal and a downlinkreception timing at which the terminal device 100A receives the downlinksignal are illustrated in FIG. 16. This point is the same as those ofthe examples illustrated in FIGS. 8, 12, and 14.

A D2D transmission timing at which the terminal device 100B transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100A actually receives the D2Dcommunication signal are also illustrated in FIG. 16. In this example,the D2D transmission timing of the terminal device 100B is almost thesame as the downlink reception timing of the terminal device 100A. As aresult, a deviation between the reception timings (that is, a deviationbetween the D2D reception timing and the downlink reception timing inthe terminal device 100A) illustrated in FIG. 16 is less than thedeviation between the reception timings illustrated in FIG. 8. In thisexample, the D2D reception timing is slightly later than the downlinkreception timing. Accordingly, when a reception period of the downlinksignal is set to be slightly longer than the length of the OFDM symbol,the terminal device 100A can properly receive the D2D communicationsignal.

FIG. 17 is a second explanatory diagram illustrating the third exampleof the D2D transmission timing according to the embodiment. In theexample of FIG. 17, the terminal device 100A is a transmission sidedevice of the D2D communication and the terminal device 100B is areception side device of the D2D communication. A downlink transmissiontiming at which the base station 200 transmits a downlink signal and adownlink reception timing at which the terminal device 100B receives thedownlink signal are illustrated in FIG. 17. This point is the same asthat of the example illustrated in FIG. 9.

A D2D transmission timing at which the terminal device 100A transmits aD2D communication signal in the D2D communication and a D2D receptiontiming at which the terminal device 100B actually receives the D2Dcommunication signal are also illustrated in FIG. 17. In this example,the D2D transmission timing of the terminal device 100A is almost thesame as the downlink reception timing of the terminal device 100B. As aresult, a deviation between the reception timings (that is, a deviationbetween the D2D reception timing and the downlink reception timing inthe terminal device 100B) illustrated in FIG. 17 is less than thedeviation between the reception timings illustrated in FIG. 9. In thisexample, the D2D reception timing is slightly later than the downlinkreception timing. Accordingly, when a reception period of the downlinksignal is set to be slightly longer than the length of the OFDM symbol,the terminal device 100B can properly receive the D2D communicationsignal.

Case of One-to-Multiple D2D Communication

Here, a D2D transmission timing of a case in which a terminal device 100performs the D2D communication with two or more other terminal devices100 will be described with reference to FIGS. 18 and 19.

FIG. 18 is an explanatory diagram illustrating a first case in which aterminal device performs D2D communication with two or more otherterminal devices. In FIG. 18, a terminal device 100B performs the D2Dcommunication with both of terminal devices 100A and 100C. As an exampleof this case, the terminal device 100B is connected to a contentdelivery server via the base station 200 and transmits content to theterminal devices 100A and 100C.

FIG. 19 is an explanatory diagram illustrating a second case in whichthe terminal device performs the D2D communication with two or moreother terminal devices. In FIG. 19, in the case of FIG. 18, the terminaldevices 100A and 100C further mutually perform the D2D communication. Asan example of this case, the terminal devices 100A, 100B, and 100Cperform communication in a group.

As described above, when the terminal device 100 performs the D2Dcommunication with two or more other terminal devices 100, it ispreferable to apply the first example or the second example of the D2Dtransmission timing described above rather than applying the thirdexample of the D2D transmission timing described above. This is becausesince the TA value of the communication partner of the D2D communicationis acquired in the third example of the D2D transmission timingdescribed above, the TA value of which the base station 200 notifiesincreases, and thus the process and communication increase and becomecomplicated.

4. FLOW OF PROCESS

Next, an example of the communication control process according to theembodiment will be described with reference to FIG. 20. FIG. 20 is asequence diagram illustrating an example of a schematic flow of thecommunication control process according to the embodiment.

In step S401, the control unit 140 of the terminal device 100A causesthe radio communication unit 120 to transmit a start request of the D2Dcommunication. Then, the base station 200 receives the start request.

Next, in step S403, the base station 200 performs paging. In the paging,information indicating the D2D communication is transmitted. Theterminal device 100B is called by the paging.

Then, in step S405, the terminal device 100B and the base station 200perform a random access procedure. During the random access procedure,the control unit 140 of the terminal device 100B causes the radiocommunication unit 120 to transmit a random access request. The basestation 200 transmits a random access response in response to the randomaccess request. The base station 200 notifies the terminal device 100Bof the TA value of the terminal device 100B in the random accessresponse.

In step S407, the transmission timing decision unit 143 of the terminaldevice 100A decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100A and the TA value acquiredin advance. For example, as in the first example of the D2D transmissiontiming described above, the downlink transmission timing of the basestation 200 calculated from the downlink reception timing and the TAvalue is decided as the D2D transmission timing of the terminal device100A.

In step S409, the transmission timing decision unit 143 of the terminaldevice 100B decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100B and the TA value acquiredin the random access procedure. For example, as in the first example ofthe D2D transmission timing described above, the downlink transmissiontiming of the base station 200 calculated from the downlink receptiontiming and the TA value is decided as the D2D transmission timing of theterminal device 100B.

In step S411 and step S413, the base station 200 instructs the terminaldevices 100A and 100B to transmit a pilot signal in the D2Dcommunication and to perform measurement in regard to the pilot signalin the D2D communication.

In step S415, the control unit 140 of the terminal device 100A causesthe radio communication unit 120 to transmit the pilot signal. Then, theradio communication unit 120 of the terminal device 100B receives thepilot signal and the control unit 140 of the terminal device 100Bperforms the measurement in regard to the pilot signal.

In step S417, the control unit 140 of the terminal device 100B causesthe radio communication unit 120 to transmit the pilot signal. The radiocommunication unit 120 of the terminal device 100A receives the pilotsignal and the control unit 140 of the terminal device 100A performs themeasurement in regard to the pilot signal.

In step S419 and step S421, the terminal devices 100A and 100B reportmeasurement results in regard to the pilot signal to the base station200 via the radio communication unit 120.

In step S423, the base station 200 determines whether to permit the D2Dcommunication based on the reported measurement results. For example,the base station 200 determines to permit the D2D communication whencommunication quality of the D2D communication satisfies a predeterminedquality requirement.

In step S425 and step S427, the base station 200 notifies the terminaldevices 100A and 100B of the permission of the D2D communication.Thereafter, the D2D communication starts between the terminal devices100A and 100B.

One example of the communication control process according to theembodiment has been described. When the third example of the D2Dtransmission timing described above is used, the base station 200notifies the terminal device 100A of the TA value of the terminal device100B before step S407 and notifies the terminal device 100B of the TAvalue of the terminal device 100A before step S409.

5. MODIFICATION EXAMPLES

Next, modification examples of the embodiment will be described withreference to FIGS. 21 to 24.

In the above-described embodiment, the example in which two terminaldevices 100 (for example, the terminal devices 100A and 100B) performingthe D2D communication are located within the same cell has beendescribed. Accordingly, examples in which two terminal devices 100performing the D2D communication are located within different cells willbe described as modification examples of the embodiment.

(Example of Cells in which Terminal Devices Performing D2D Communicationare Located)

First, a specific example of cells which is a premise will be describedwith reference to FIGS. 21 and 22.

FIG. 21 is an explanatory diagram illustrating a first example of cellswhen the terminal devices performing the D2D communication are locatedin the different cells. Adjacent cells 21A and 20B are illustrated inFIG. 21. The base station 200A of the cell 21A and the terminal device100A located in the cell 21A are illustrated. The base station 200B ofthe cell 21B and the terminal device 100B located in the cell 21B areillustrated. For example, thus, the terminal devices 100 performing theD2D communication are located in the two mutually adjacent cells 21.

FIG. 22 is an explanatory diagram illustrating a second example of cellswhen the terminal devices performing the D2D communication are locatedin the different cells. A macro cell 23 and a small cell 25 overlappingwith the macro cell 23 are illustrated in FIG. 22. A base station 203 ofthe macro cell 23 and the terminal device 100A located within the macrocell 23 are illustrated. A base station 205 of the small cell 25 and theterminal device 100B located within the small cell 25 are illustrated.For example, thus, the terminal devices 100 performing the D2Dcommunication are located in the macro cell 23 and the small cell 25,respectively.

As in the above-described example, even when two terminal devices 100performing the D2D communication are located within different cells, aproper D2D transmission timing can be decided. Modification examples ofthe embodiment will be described below using the example of FIG. 21 asthe premise. This description can also be applied similarly to theexample of FIG. 22.

Since a decision scheme when transmission and reception timings betweentwo cells are synchronized and a decision scheme when transmission andreception timings between two cells are not synchronized are slightlydifferent, the two cases will be described.

(When Synchronization is Achieved Between Cells)

When the synchronization is achieved between the cells, the downlinktransmission timings by the base station 200 between the cells 21 arethe same. As in the case in which two terminal devices 100 performingthe D2D communication are located in the same cell, the D2D transmissiontiming can be decided. For example, as in the first to third examples ofthe D2D transmission timing described above, the D2D transmission timingcan be decided.

In the third example of the D2D transmission timing, as described above,the terminal device 100A (the transmission timing decision unit 143)decides the D2D transmission timing based on the downlink receptiontiming of the terminal device 100A, the TA information of the terminaldevice 100A, and the TA information of the other terminal device 100B.The TA information of the terminal device 100A is TA information of theterminal device 100A in the cell 21A in which the terminal device 100 islocated. On the other hand, when the terminal devices 100A and 100Bperforming the D2D communication are located within different cells, theTA information of the terminal device 100B is TA information of theterminal device 100B in the cell 21B in which the terminal device 100Bis located. Therefore, the base station 200B transmits the TAinformation of the terminal device 100B to the base station 200A, andthen the base station 200A transmits the TA information of the terminaldevice 100B to the terminal device 100A. Then, the terminal device 100A(the information acquisition unit 141) acquires the TA information ofthe terminal device 100B.

(When Synchronization is not Achieved Between Cells)

When the synchronization is not achieved between the cells, the downlinktransmission timings by the base station 200 between the cells 21 aredifferent. Therefore, the followings are different compared to the casein which two terminal devices 100 performing the D2D communication arelocated in the same cell.

First Example of D2D Transmission Timing

In the first example of the D2D transmission timing, as described above,the terminal device 100A decides the D2D transmission timing based onthe downlink reception timing of the terminal device 100A and the TAinformation of the terminal device 100A. When the terminal devices 100Aand 100B performing the D2D communication are located within differentcells, the downlink reception timing of the terminal device 100A and theTA information of the terminal device 100A are as follows.

First, the downlink reception timing of the terminal device 100A is areception timing at which the terminal device 100A receives the downlinksignal (that is, the downlink signal of the cell 21B) from the basestation 200B performing radio communication with the terminal device100B. Therefore, the information acquisition unit 141 of the terminaldevice 100A causes the radio communication unit 120 to receive thedownlink signal (for example, a primary synchronization signal, asecondary synchronization signal, or the like) of the cell 21B andacquires the reception timing of the downlink signal.

The TA information of the terminal device 100A is TA information (thatis, TA information of the terminal device 100A in the cell 21B) used todecide a timing at which the terminal device 100A transmits an uplinksignal to the base station 200B. Therefore, the information acquisitionunit 141 causes the terminal device 100A to perform random access to thecell 21B and acquires the TA information of the terminal device 100A inthe cell 21B.

According to the downlink reception timing of the terminal device 100Aand the TA information of the terminal device 100A, the terminal device100A can calculate, for example, a timing at which the base station 200Btransmits the downlink signal. That is, the terminal device 100A cancalculate the downlink transmission timing in the cell 21B in which theterminal device 100B which is a partner side device of the D2Dcommunication is located.

Using the fact that the terminal devices 100A and 100B are locatednearby as the premise, the information acquisition unit 141 may acquireand use the TA information of the terminal device 100B in the cell 21Bas a substitute of the TA information of the terminal device 100A in thecell 21B. In this case, the base station 200B may transmit the TAinformation of the terminal device 100B to the base station 200A and thebase station 200A may transmit the TA information of the terminal device100B to the terminal device 100A.

Second Example of D2D Transmission Timing

In the second example of the D2D transmission timing, as describedabove, the terminal device 100A decides the D2D transmission timingbased on the downlink reception timing of the terminal device 100A. Whenthe terminal devices 100A and 100B performing the D2D communication arelocated within different cells, the downlink reception timing of theterminal device 100A is as follows.

As in the first example of the D2D transmission timing described above,the downlink reception timing of the terminal device 100A is a receptiontiming at which the terminal device 100A receives the downlink signal ofthe cell 21B.

According to the downlink reception timing of the terminal device 100A,the terminal device 100A can know a reception timing at which theterminal device 100A receives the downlink signal from the base station21B. That is, the terminal device 100A can calculate the downlinktransmission timing in the cell 21B in which the terminal device 100Bwhich is a partner side device of the D2D communication is located.

Third Example of D2D Transmission Timing

In the third example of the D2D transmission timing, as described above,the terminal device 100A decides the D2D transmission timing based onthe downlink reception timing of the terminal device 100A, the TAinformation of the terminal device 100A, and the TA information of theterminal device 100B. When the terminal devices 100A and 100B performingthe D2D communication are located within different cells, the downlinkreception timing of the terminal device 100A, the TA information of theterminal device 100A, the TA information of the terminal device 100B areas follows.

First, the downlink reception timing of the terminal device 100A is areception timing at which the terminal device 100A receives the downlinksignal of the cell 21B as in the first example of the D2D transmissiontiming described above. The TA information of the terminal device 100Ais TA information of the terminal device 100A in the cell 21B as in thefirst example of the D2D transmission timing described above.

The TA information of the terminal device 100B is TA information (thatis, TA information of the terminal device 100B in the cell 21B) used todecide a timing at which the terminal device 100B transmits an uplinksignal to the base station 200B. Therefore, the base station 200Btransmits the TA information of the terminal device 100B to the basestation 200A and the base station 200A transmits the TA information ofthe terminal device 100B to the terminal device 100A. Then, theinformation acquisition unit 141 acquires the TA information of theterminal device 100B.

According to the downlink reception timing of the terminal device 100A,the TA information of the terminal device 100A, and the TA informationof the terminal device 100B, the terminal device 100A can calculate, forexample, a timing at which the terminal device 100B which is a partnerside device of the D2D communication receives the downlink signal fromthe base station 200B. That is, the terminal device 100A can calculate atiming at which the terminal device 100B receives the downlink signal ofthe cell 21B.

(Flow of Process)

Next, examples of the communication control process according tomodification examples of the embodiment will be described with referenceto FIGS. 23 and 24.

When Synchronization is Achieved Between Cells

FIG. 23 is a sequence diagram illustrating a first example of aschematic flow of the communication control process according to amodification example of the embodiment.

In step S501, the control unit 140 of the terminal device 100A causesthe radio communication unit 120 to transmit a start request of the D2Dcommunication. Then, the base station 200A receives the start request.Then, in step S503, the base station 200A transmits the start request tothe base station 200B.

In step S505, the base station 200A transmit inter-cell synchronizationinformation indicating whether the cells 21A and 21B are synchronized,to the terminal device 100A. In this case, the inter-cellsynchronization information indicates that the cells 21A and 21B aresynchronized. In this way, the terminal device 100A knows that the cells21A and 21B are synchronized. In this example, the inter-cellsynchronization information is acquired in step S505, but theacquisition of the inter-cell synchronization information is not limitedto this example. The inter-cell synchronization information may beannounced in advance using the system information to the terminal device100 or may be announced in advance separately using signaling from thebase station 200 to the terminal device 100. When all of the cells orsome of the cells in the system are synchronized, information regardingwhether synchronization is achieved between the cells may be stored inthe terminal devices 100.

In step S507, the base station 200B perform paging. In the paging,information indicating the D2D communication is transmitted. Theterminal device 100B is called by the paging.

Then, in step S509, the terminal device 100B and the base station 200Bperform a random access procedure. During the random access procedure,the control unit 140 of the terminal device 100B causes the radiocommunication unit 120 to transmit a random access request. The basestation 200B transmits a random access response in response to therandom access request. The base station 200B notifies the terminaldevice 100B of the TA value of the terminal device 100B in the randomaccess response. The TA value is the TA value of the terminal device100B in the cell 21B.

In step S511, the transmission timing decision unit 143 of the terminaldevice 100A decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100A in the cell 21A and the TAvalue (the TA value of the terminal device 100A in the cell 21A)acquired in advance. For example, as in the first example of the D2Dtransmission timing described above, the downlink transmission timing ofthe base station 200A calculated from the downlink reception timing andthe TA value is decided as the D2D transmission timing of the terminaldevice 100A.

In step S513, the transmission timing decision unit 143 of the terminaldevice 100B decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100B in the cell 21B and the TAvalue (the TA value of the terminal device 100B in the cell 21B)acquired in the random access procedure. For example, as in the firstexample of the D2D transmission timing described above, the downlinktransmission timing of the base station 200B calculated from thedownlink reception timing and the TA value is decided as the D2Dtransmission timing of the terminal device 100B.

In step S515, the base station 200A instructs the terminal device 100Ato transmit the pilot signal in the D2D communication and performmeasurement in regard to the pilot signal in the D2D communication.

In step S517, the base station 200B instructs the terminal device 100Bto transmit the pilot signal in the D2D communication and performmeasurement in regard to the pilot signal in the D2D communication.

In step S519, the control unit 140 of the terminal device 100A causesthe radio communication unit 120 to transmit the pilot signal. Then, theradio communication unit 120 of the terminal device 100B receives thepilot signal and the control unit 140 of the terminal device 100Bperforms the measurement in regard to the pilot signal.

In step S521, the control unit 140 of the terminal device 100B causesthe radio communication unit 120 to transmit the pilot signal. The radiocommunication unit 120 of the terminal device 100A receives the pilotsignal and the control unit 140 of the terminal device 100A performs themeasurement in regard to the pilot signal.

In step S523, the terminal device 100B reports a measurement result inregard to the pilot signal to the base station 200B via the radiocommunication unit 120.

In step S525, the terminal device 100A reports a measurement result inregard to the pilot signal to the base station 200A via the radiocommunication unit 120.

In step S527, the base stations 200A and 200B determine whether topermit the D2D communication based on the reported measurement results.For example, the base stations 200A and 200B determine to permit the D2Dcommunication when communication quality of the D2D communicationsatisfies a predetermined quality requirement.

In step S529, the base station 200A notifies the terminal device 100A ofthe permission of the D2D communication. In step S531, the base station200B notifies the terminal device 100B of the permission of the D2Dcommunication. Thereafter, the D2D communication starts between theterminal devices 100A and 100B.

The first example of the communication control process according to themodification example of the embodiment has been described. When thethird example of the D2D transmission timing described above is used,the base station 200A notifies the terminal device 100A of the TA valueof the terminal device 100B in the cell 21B before step S511. The basestation 200B notifies the terminal device 100B of the TA value of theterminal device 100A in the cell 21A before step S513.

When Synchronization is not Achieved Between Cells

FIG. 24 is a sequence diagram illustrating a second example of theschematic flow of the communication control process according to amodification example of the embodiment. Here, only step S551, step S553,step S555, step S557, and step S559 which are differences between thefirst example of the schematic flow of the communication control processillustrated in FIG. 23 and the second example of the schematic flow ofthe communication control process illustrated in FIG. 24 will bedescribed.

In step S551, the base station 200A transmits inter-cell synchronizationinformation indicating whether the cells 21A and 21B are synchronized,to the terminal device 100A. In this example, the inter-cellsynchronization information indicates that the cells 21A and 21B are notsynchronized. In this way, the terminal device 100A knows that the cells21A and 21B are not synchronized. In this example, the inter-cellsynchronization information is acquired in step S551, but theacquisition of the inter-cell synchronization information is not limitedto this example. The inter-cell synchronization information may beannounced in advance using the system information to the terminal device100 or may be announced in advance separately using signaling from thebase station 200 to the terminal device 100. When all of the cells orsome of the cells in the system are synchronized, information regardingwhether synchronization is achieved between the cells may be stored inthe terminal devices 100.

Then, in step S553, the terminal device 100A and the base station 200Bperform a random access procedure. During the random access procedure,the control unit 140 of the terminal device 100A causes the radiocommunication unit 120 to transmit a random access request. The basestation 200B transmits a random access response in response to therandom access request. The base station 200B notifies the terminaldevice 100A of the TA value of the terminal device 100A in the randomaccess response. The TA value is the TA value of the terminal device100A in the cell 21B.

Then, in step S555, the terminal device 100B and the base station 200Aperform a random access procedure. During the random access procedure,the control unit 140 of the terminal device 100B causes the radiocommunication unit 120 to transmit a random access request. The basestation 200A transmits a random access response in response to therandom access request. The base station 200A notifies the terminaldevice 100B of the TA value of the terminal device 100B in the randomaccess response. The TA value is the TA value of the terminal device100B in the cell 21A.

In step S557, the transmission timing decision unit 143 of the terminaldevice 100A decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100A in the cell 21B and the TAvalue (the TA value of the terminal device 100A in the cell 21B)acquired in the random access procedure. For example, as in the firstexample of the D2D transmission timing described above, the downlinktransmission timing of the base station 200B calculated from thedownlink reception timing and the TA value is decided as the D2Dtransmission timing of the terminal device 100A.

In step S559, the transmission timing decision unit 143 of the terminaldevice 100B decides the D2D transmission timing based on the downlinkreception timing of the terminal device 100B in the cell 21A and the TAvalue (the TA value of the terminal device 100B in the cell 21A)acquired in the random access procedure. For example, as in the firstexample of the D2D transmission timing described above, the downlinktransmission timing of the base station 200A calculated from thedownlink reception timing and the TA value is decided as the D2Dtransmission timing of the terminal device 100B.

The second example of the communication control process according to themodification example of the embodiment has been described. When thethird example of the D2D transmission timing described above is used,the base station 200A notifies the terminal device 100A of the TA valueof the terminal device 100B in the cell 21B before step S557. The basestation 200B notifies the terminal device 100B of the TA value of theterminal device 100A in the cell 21A before step S559.

6. APPLICATION

The technology related to the present disclosure can be applied tovarious products. The terminal device 100 may be realized as, forexample, a mobile terminal such as a smartphone, a tablet personalcomputer (PC), a notebook PC, a portable game console, aportable/dongle-style mobile router, or a digital camera, or as anin-vehicle terminal such as a car navigation device. In addition, theterminal device 100 may also be realized as a terminal that conductsmachine-to-machine (M2M) communication (also called a machine-typecommunication (MTC) terminal). Furthermore, the terminal device 100 maybe a radio communication module mounted onboard these terminals (forexample, an integrated circuit module configured on a single die).

For example, the base station 200 may be realized as one kind of evolvedNodeB (eNB) such as a macro eNB or a small eNB. The small eNB may be aneNB that covers a smaller cell, such as a pico eNB, a micro eNB, or ahome (pemto) eNB, than a macro cell. Instead, the base station 200 maybe realized as another kind of base station such as a NodeB or a basetransceiver station (BTS). The base station 200 may include a main body(also referred to as a base station device) controlling radiocommunication and at least one remote radio head (RRH) disposed at adifferent location than the main body. The above-described various kindsof terminals may perform a base station function temporarily orsemi-permanently to operate as the base station 200.

<<6.1. Applications Related to Terminal Device>> (First Application)

FIG. 25 is a block diagram illustrating an example of a schematicconfiguration of a smartphone 900 to which technology according to anembodiment of the present disclosure may be applied. The smartphone 900is equipped with a processor 901, memory 902, storage 903, an externalconnection interface 904, a camera 906, a sensor 907, a microphone 908,an input device 909, a display device 910, a speaker 911, a radiocommunication interface 912, one or more antenna switches 915, one ormore antennas 916, a bus 917, a battery 918, and an auxiliary controller919.

The processor 901 may be a CPU or system-on-a-chip (SoC), for example,and controls functions in the application layer and other layers of thesmartphone 900. The memory 902 includes RAM and ROM, and stores programsexecuted by the processor 901 as well as data. The storage 903 mayinclude a storage medium such as semiconductor memory or a hard disk.The external connection interface 904 is an interface for connecting anexternally attached device, such as a memory card or Universal SerialBus (USB) device, to the smartphone 900.

The camera 906 includes an image sensor such as a charge-coupled device(CCD) or complementary metal-oxide-semiconductor (CMOS) sensor, andgenerates a captured image. The sensor 907 may include a sensor groupsuch as a positioning sensor, a gyro sensor, a geomagnetic sensor, andan acceleration sensor, for example. The microphone 908 converts audioinput into the smartphone 900 into an audio signal. The input device 909includes devices such as a touch sensor that detects touches on a screenof the display device 910, a keypad, a keyboard, buttons, or switches,and receives operations or information input from a user. The displaydevice 910 includes a screen such as a liquid crystal display (LCD) oran organic light-emitting diode (OLED) display, and displays an outputimage of the smartphone 900. The speaker 911 converts an audio signaloutput from the smartphone 900 into audio.

The radio communication interface 912 supports a cellular communicationscheme such as LTE or LTE-Advanced, and executes radio communication.Typically, the radio communication interface 912 may include a BBprocessor 913, an RF circuit 914, and the like. The BB processor 913 mayconduct processes such as encoding/decoding, modulation/demodulation,and multiplexing/demultiplexing, for example, and executes varioussignal processing for radio communication. Meanwhile, the RF circuit 914may include components such as a mixer, a filter, and an amp, andtransmits or receives a radio signal via an antenna 916. The radiocommunication interface 912 may also be a one-chip module integratingthe BB processor 913 and the RF circuit 914. The radio communicationinterface 912 may also include a plurality of BB processors 913 and aplurality of RF circuits 914 as illustrated in FIG. 25. Note thatalthough FIG. 25 illustrates an example of the radio communicationinterface 912 including a plurality of BB processors 913 and a pluralityof RF circuits 914, the radio communication interface 912 may alsoinclude a single BB processor 913 or a single RF circuit 914.

Furthermore, in addition to a cellular communication scheme, the radiocommunication interface 912 may also support other types of radiocommunication schemes such as a short-range wireless communicationscheme, a near field wireless communication scheme, or a wireless localarea network (LAN) scheme. In this case, a BB processor 913 and an RFcircuit 914 may be included for each radio communication scheme.

Each antenna switch 915 switches the destination of an antenna 916 amonga plurality of circuits included in the radio communication interface912 (for example, circuits for different radio communication schemes).

Each antenna 916 includes a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used by the radio communication interface 912 totransmit and receive radio signals. The smartphone 900 may also includea plurality of antennas 916 as illustrated in FIG. 25. Note thatalthough FIG. 25 illustrates an example of the smartphone 900 includinga plurality of antennas 916, the smartphone 900 may also include asingle antenna 916.

Furthermore, the smartphone 900 may also be equipped with an antenna 916for each radio communication scheme. In this case, the antenna switch915 may be omitted from the configuration of the smartphone 900.

The bus 917 interconnects the processor 901, the memory 902, the storage903, the external connection interface 904, the camera 906, the sensor907, the microphone 908, the input device 909, the display device 910,the speaker 911, the radio communication interface 912, and theauxiliary controller 919. The battery 918 supplies electric power to therespective blocks of the smartphone 900 illustrated in FIG. 25 via powersupply lines partially illustrated with dashed lines in the drawing. Theauxiliary controller 919 causes minimal functions of the smartphone 900to operate while in a sleep mode, for example.

In the smartphone 900 illustrated in FIG. 25, the informationacquisition unit 141 and the transmission timing decision unit 143described with reference to FIG. 11 may be implemented in the radiocommunication interface 912. Also, at least some of these functions mayalso be implemented in the processor 901 or the auxiliary controller919.

(Second Application)

FIG. 26 is a block diagram illustrating an example of a schematicconfiguration of a car navigation device 920 to which technologyaccording to an embodiment of the present disclosure may be applied. Thecar navigation device 920 is equipped with a processor 921, memory 922,a Global Positioning System (GPS) module 924, a sensor 925, a datainterface 926, a content player 927, a storage medium interface 928, aninput device 929, a display device 930, a speaker 931, a radiocommunication interface 933, one or more antenna switches 936, one ormore antennas 937, and a battery 938.

The processor 921 may be a CPU or SoC, for example, and controls a carnavigation function and other functions of the car navigation device920. The memory 922 includes RAM and ROM, and stores programs executedby the processor 921 as well as data.

The GPS module 924 measures the position of the car navigation device920 (for example, the latitude, longitude, and altitude) by using GPSsignals received from GPS satellites. The sensor 925 may include asensor group such as a gyro sensor, a geomagnetic sensor, and abarometric pressure sensor, for example. The data interface 926 isconnected to an in-vehicle network 941 via a port not illustrated in thedrawing, and acquires data generated on the vehicle side, such asvehicle speed data.

The content player 927 plays content stored on a storage medium (forexample, a CD or DVD) inserted into the storage medium interface 928.The input device 929 includes devices such as a touch sensor thatdetects touches on a screen of the display device 930, buttons, orswitches, and receives operations or information input from a user. Thedisplay device 930 includes a screen such as an LCD or OLED display, anddisplays a navigation function or an image of played-back content. Thespeaker 931 outputs audio of a navigation function or played-backcontent.

The radio communication interface 933 supports a cellular communicationscheme such as LTE or LTE-Advanced, and executes radio communication.Typically, the radio communication interface 933 may include a BBprocessor 934, an RF circuit 935, and the like. The BB processor 934 mayconduct processes such as encoding/decoding, modulation/demodulation,and multiplexing/demultiplexing, for example, and executes varioussignal processing for radio communication. Meanwhile, the RF circuit 935may include components such as a mixer, a filter, and an amp, andtransmits or receives a radio signal via an antenna 937. The radiocommunication interface 933 may also be a one-chip module integratingthe BB processor 934 and the RF circuit 935. The radio communicationinterface 933 may also include a plurality of BB processors 934 and aplurality of RF circuits 935 as illustrated in FIG. 26. Note thatalthough FIG. 26 illustrates an example of the radio communicationinterface 933 including a plurality of BB processors 934 and a pluralityof RF circuits 935, the radio communication interface 933 may alsoinclude a single BB processor 934 or a single RF circuit 935.

Furthermore, in addition to a cellular communication scheme, the radiocommunication interface 933 may also support other types of radiocommunication schemes such as a short-range wireless communicationscheme, a near field wireless communication scheme, or a wireless LANscheme. In this case, a BB processor 934 and an RF circuit 935 may beincluded for each radio communication scheme.

Each antenna switch 936 switches the destination of an antenna 937 amonga plurality of circuits included in the radio communication interface933 (for example, circuits for different radio communication schemes).

Each antenna 937 includes a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used by the radio communication interface 933 totransmit and receive radio signals. The car navigation device 920 mayalso include a plurality of antennas 937 as illustrated in FIG. 26. Notethat although FIG. 26 illustrates an example of the car navigationdevice 920 including a plurality of antennas 937, the car navigationdevice 920 may also include a single antenna 937.

Furthermore, the car navigation device 920 may also be equipped with anantenna 937 for each radio communication scheme. In this case, theantenna switch 936 may be omitted from the configuration of the carnavigation device 920.

The battery 938 supplies electric power to the respective blocks of thecar navigation device 920 illustrated in FIG. 26 via power supply linespartially illustrated with dashed lines in the drawing. Also, thebattery 938 stores electric power supplied from the vehicle.

In the car navigation device 920 illustrated in FIG. 26, the informationacquisition unit 141 and the transmission timing decision unit 143described with reference to FIG. 11 may be implemented in the radiocommunication interface 933. Also, at least some of these functions mayalso be implemented in the processor 921.

In addition, technology according to the present disclosure may also berealized as an in-vehicle system (or vehicle) 940 that includes one ormore blocks of the car navigation device 920 discussed above, thein-vehicle network 941, and a vehicle-side module 942. The vehicle-sidemodule 942 generates vehicle-side data such as the vehicle speed, numberof engine revolutions, or malfunction information, and outputs thegenerated data to the in-vehicle network 941.

<<10.1. Applications Related to Base Station>> (First Application)

FIG. 27 is a block diagram illustrating a first example of a schematicconfiguration of an eNB to which technology according to an embodimentof the present disclosure may be applied. An eNB 800 includes one ormore antennas 810, and a base station device 820. The respectiveantennas 810 and the base station device 820 may be connected to eachother via an RF cable.

Each antenna 810 includes a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used by the base station device 820 to transmit andreceive radio signals. The eNB 800 may include a plurality of antennas810 as illustrated in FIG. 27, and the plurality of antennas 810 mayrespectively correspond to a plurality of frequency bands used by theeNB 800, for example. Note that although FIG. 27 illustrates an exampleof the eNB 800 including a plurality of antennas 810, the eNB 800 mayalso include a single antenna 810.

The base station device 820 is equipped with a controller 821, memory822, a network interface 823, and a radio communication interface 825.

The controller 821 may be a CPU or DSP, for example, and causes varioushigher-layer functions of the base station device 820 to operate. Forexample, the controller 821 generates a data packet from data inside asignal processed by the radio communication interface 825, and forwardsthe generated packet via the network interface 823. The controller 821may also generate a bundled packet by bundling data from a plurality ofbaseband processors, and forward the generated bundled packet. Inaddition, the controller 821 may also include logical functions thatexecute controls such as Radio Resource Control (RRC), Radio Bearercontrol, mobility management, admission control, or scheduling. Also,such controls may also be executed in coordination with a nearby eNB orcore network node. The memory 822 includes RAM and ROM, and storesprograms executed by the controller 821 as well as various control data(such as a terminal list, transmit power data, and scheduling data, forexample).

The network interface 823 is a communication interface for connectingthe base station device 820 to a core network 824. The controller 821may also communication with a core network node or another eNB via thenetwork interface 823. In this case, the eNB 800 and the core networknode or other eNB may be connected to each other by a logical interface(for example, the S1 interface or the X2 interface). The networkinterface 823 may also be a wired communication interface, or a wirelesscommunication interface for wireless backhaul. In the case in which thenetwork interface 823 is a wireless communication interface, the networkinterface 823 may use a higher frequency band for wireless communicationthan the frequency band used by the radio communication interface 825.

The radio communication interface 825 supports a cellular communicationscheme such as Long Term Evolution (LTE) or LTE-Advanced, and provides aradio connection to a terminal positioned inside the cell of the eNB 800via an antenna 810.

Typically, the radio communication interface 825 may include a baseband(BB) processor 826, an RF circuit 827, and the like. The BB processor826 may conduct processes such as encoding/decoding,modulation/demodulation, and multiplexing/demultiplexing, for example,and executes various signal processing in respective layers (forexample, L1, Medium Access Control (MAC), Radio Link Control (RLC), andPacket Data Convergence Protocol (PDCP)). The BB processor 826 may alsoinclude some or all of the logical functions discussed earlier insteadof the controller 821. The BB processor 826 may be a module includingmemory that stores a communication control program, a processor thatexecutes such a program, and related circuits. The functions of the BBprocessor 826 may also be modifiable by updating the program. Also, themodule may be a card or a blade inserted into a slot of the base stationdevice 820, or a chip mounted onboard the card or the blade. Meanwhile,the RF circuit 827 may include components such as a mixer, a filter, andan amp, and transmits or receives a radio signal via an antenna 810.

The radio communication interface 825 may also include a plurality of BBprocessors 826 as illustrated in FIG. 27, and the plurality of BBprocessors 826 may respectively correspond to a plurality of frequencybands used by the eNB 800, for example. In addition, the radiocommunication interface 825 may also include a plurality of RF circuits827 as illustrated in FIG. 27, and the plurality of RF circuits 827 mayrespectively correspond to a plurality of antenna elements, for example.Note that although FIG. 27 illustrates an example of the radiocommunication interface 825 including a plurality of BB processors 826and a plurality of RF circuits 827, the radio communication interface825 may also include a single BB processor 826 or a single RF circuit827.

(Second Application)

FIG. 28 is a block diagram illustrating a second example of a schematicconfiguration of an eNB to which technology according to an embodimentof the present disclosure may be applied. An eNB 830 includes one ormore antennas 840, a base station device 850, and an RRH 860. Therespective antennas 840 and the RRH 860 may be connected to each othervia an RF cable. Also, the base station device 850 and the RRH 860 maybe connected to each other by a high-speed link such as an optical fibercable.

Each antenna 840 includes a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used by the RRH 860 to transmit and receive radiosignals. The eNB 830 may include a plurality of antennas 840 asillustrated in FIG. 28, and the plurality of antennas 840 mayrespectively correspond to a plurality of frequency bands used by theeNB 830, for example. Note that although FIG. 28 illustrates an exampleof the eNB 830 including a plurality of antennas 840, the eNB 830 mayalso include a single antenna 840.

The base station device 850 is equipped with a controller 851, memory852, a network interface 853, a radio communication interface 855, and aconnection interface 857. The controller 851, the memory 852, and thenetwork interface 853 are similar to the controller 821, the memory 822,and the network interface 823 described with reference to FIG. 27.

The radio communication interface 855 supports a cellular communicationscheme such as LTE or LTE-Advanced, and provides a radio connection to aterminal positioned inside a sector corresponding to the RRH 860 via theRRH 860 and an antenna 840. Typically, the radio communication interface855 may include a BB processor 856 and the like. The BB processor 856 issimilar to the BB processor 826 described with reference to FIG. 27,except for being connected to an RF circuit 864 of the RRH 860 via theconnection interface 857. The radio communication interface 855 may alsoinclude a plurality of BB processors 856 as illustrated in FIG. 28, andthe plurality of BB processors 856 may respectively correspond to aplurality of frequency bands used by the eNB 830, for example. Note thatalthough FIG. 28 illustrates an example of the radio communicationinterface 855 including a plurality of BB processors 856, the radiocommunication interface 855 may also include a single BB processor 856.

The connection interface 857 is an interface for connecting the basestation device 850 (radio communication interface 855) to the RRH 860.The connection interface 857 may also be a communication module forcommunication on the high-speed link connecting the base station device850 (radio communication interface 855) and the RRH 860.

In addition, the RRH 860 is equipped with a connection interface 861 anda radio communication interface 863.

The connection interface 861 is an interface for connecting the RRH 860(radio communication interface 863) to the base station device 850. Theconnection interface 861 may also be a communication module forcommunication on the high-speed link.

The radio communication interface 863 transmits and receives a radiosignal via an antenna 840. Typically, the radio communication interface863 may include an RF circuit 864. The RF circuit 864 may includecomponents such as a mixer, a filter, and an amp, and transmits orreceives a radio signal via an antenna 840. The radio communicationinterface 863 may also include a plurality of RF circuits 864 asillustrated in FIG. 28, and the plurality of RF circuits 864 mayrespectively correspond to a plurality of antenna elements, for example.Note that although FIG. 28 illustrates an example of the radiocommunication interface 863 including a plurality of RF circuits 864,the radio communication interface 863 may also include a single RFcircuit 864.

The example in which the terminal device 100 decides the D2Dtransmission timing of the own device has been described. However,instead of the terminal device 100, the base station 200 may decide aD2D transmission timing of the terminal device 100 and notify theterminal device 100 of the transmission timing. That is, the informationacquisition unit 141 and the transmission timing decision unit 143descried with reference to FIG. 11 may not be included by terminaldevice 100, but may be instead included by the base station 200. In thiscase, in the eNB 800 and the eNB 830 illustrated in FIGS. 28 and 29, theinformation acquisition unit 141 and the transmission timing decisionunit 143 described with reference to FIG. 11 may be implemented in theradio communication interface 825 as well as the radio communicationinterface 855 and/or the radio communication interface 863. Also, atleast some of these functions may also be implemented in the controller821 and the controller 851.

7. CONCLUSION

The communication devices and each process according to the embodimenthave been described above with reference to FIGS. 1 to 24. According tothe embodiment of the present disclosure, the reception timing (that is,the downlink reception timing) at which the terminal device 100 receivesthe downlink signal from the base station 200 performing the radiocommunication with the terminal device 100 or the other terminal device100 is acquired. The transmission timing (that is, the D2D transmissiontiming) at which the terminal device 100 performing the D2Dcommunication transmits a signal to the other terminal device 100 isdecided based on the acquired reception timing. Then, the decided D2Dtransmission timing is a timing later than the timing (that is, theuplink transmission timing) at which the terminal device 100 transmitsthe uplink signal.

When the D2D transmission timing of a transmission side device of theD2D communication is the same as the uplink transmission timing, the D2Dcommunication signal may arrive at a reception side device quite earlierthan the downlink reception timing of the reception side device of theD2D communication. For this reason, there is a possibility of a portionother than the CP in the D2D communication signal not being demodulatedaccording to distances between the base station 200, and the receptionside device and the transmission side device and the distance betweenthe reception side device and the transmission side device.

On the other hand, in the embodiment, when the D2D transmission timingis a timing later than the uplink transmission timing, the downlinkreception timing and the D2D reception timing of a partner side arecloser. Accordingly, there is a high possibility of the D2Dcommunication signal being properly received. In other words, it ispossible to loosen constraints (for example, the distances between thebase station 200, and the reception side device and the transmissionside device and the distance between the reception side device and thetransmission side device) for proper reception of the D2D communicationsignal. As a result, off-loading can be performed more effectively,which considerably contributes to an increase a system capacity.

For example, the TA information used to decide the timing (that is, theuplink transmission timing) at which the terminal device 100 transmitsthe uplink signal is further acquired. As the first example of the D2Dtransmission timing, the D2D transmission timing is decided based on thedownlink reception timing of the terminal device 100 and the TAinformation of the terminal device 100.

Since the TA information (for example, the TA value) is an existingparameter of which the terminal device 100 is notified at the time ofthe random access, it is not necessary for the base station 200 totransmit a new control signal.

For example, the decided D2D transmission timing is the timing earlierthan the downlink reception timing.

In this way, it is possible to prevent a period in which the partnerdevice actually receives the D2D communication signal from not enteringa period in which the partner device actually receives the downlinksignal because the D2D transmission timing is too late.

For example, the decided D2D transmission timing is a timing later thana timing (hereinafter referred to as a “downlink transmission timing”)at which the base station 200 transmits the downlink signal. Forexample, the downlink transmission timing is a timing earlier than thedownlink reception timing by half of the time corresponding to the TAinformation of the terminal device 100.

In this way, the D2D transmission timing is later than the downlinktransmission timing of the base station. Since the downlink receptiontiming of the partner device is at least later than the downlinktransmission timing, the downlink reception timing and the D2Dtransmission timing of the partner side are closer. Accordingly, thereis a high possibility of the D2D communication signal being properlyreceived. In other words, it is possible to loosen the constraints (forexample, the distances between the base station 200, and the receptionside device and the transmission side device and the distance betweenthe reception side device and the transmission side device) for properreception of the D2D communication signal.

As a specific example, the decided D2D transmission timing is a timing(that is, the downlink transmission timing) at which the base station200 transmits the downlink signal.

In this way, the D2D transmission timing becomes nearly constant betweenthe terminal devices 100. That is, a variation in the D2D transmissiontiming by the terminal device 100 is small irrespective of the positionof each terminal device 100 within the cell 21, a frequency band usedfor the D2D communication, and a duplex communication scheme (forexample, an FDD scheme or a TDD scheme).

As the second example of the D2D transmission timing, the decided D2Dtransmission timing is the reception timing (that is, the downlinkreception timing) at which the terminal device 100 receives the downlinksignal.

In general, the terminal devices 100 (for example, the terminals 100Aand 100B) performing the D2D communication are located nearby. That is,the distance between the terminal devices 100 is small. Therefore, adifference between the downlink reception timing of the transmissionside device and the downlink reception timing of the reception side inthe D2D communication is small. Further, in the D2D communication,propagation delay from the transmission side device to the receptionside device is small. Accordingly, when the transmission side device(for example, the terminal device 100A) of the D2D communicationtransmits a D2D communication signal at a downlink reception timing ofthe own device, the reception side device (for example, the terminaldevice 100B) can receive the D2D communication signal at a timing closeto the downlink reception timing of the own device. Accordingly, thereis a high possibility of the D2D communication signal being properlyreceived. In other words, it is possible to loosen the constraints (forexample, the distances between the base station 200, and the receptionside device and the transmission side device and the distance betweenthe reception side device and the transmission side device) for properreception of the D2D communication signal.

In this case, information other than the reception timing is notnecessary. Accordingly, even when the TA value is not yet acquired (forexample, the terminal device 100 does not perform random access and isin an idle state), the terminal device 100 can transmit the D2Dcommunication signal at a proper D2D transmission timing.

As the third example of the D2D transmission timing, the TA informationused to decide the timing (that is, the uplink transmission timing ofanother terminal device 100) at which the other terminal device 100transmits the uplink signal is further acquired. The D2D transmissiontiming is decided based on the downlink reception timing of the terminaldevice 100, the TA information of the terminal device 100, and the TAinformation of the other terminal device 100.

More specifically, for example, the decided D2D transmission timing isthe timing (that is, the downlink reception timing of the other terminaldevice 100) at which the other terminal device 100 (that is, thereception side terminal device of the D2D communication) receives thedownlink signal from the base station 200. For example, the downlinkreception timing of the other terminal device 100 is the timing laterthan a timing (that is, a downlink transmission timing) at which thebase station 200 transmits the downlink signal by half of a timecorresponding to the TA information of the other terminal device 100.

In general, the terminal devices 100 (for example, the terminals 100Aand 100B) performing the D2D communication are located nearby. That is,the distance between the terminal devices 100 is small. Therefore, inthe D2D communication, propagation delay from the transmission sidedevice to the reception side device is small. Accordingly, when thetransmission side device (for example, the terminal device 100A) of theD2D communication transmits a D2D communication signal at the downlinkreception timing of the reception side device (for example, the terminaldevice 100B), the reception side device can receive the D2Dcommunication signal at the timing close to the downlink receptiontiming of the own device. Accordingly, there is a high possibility ofthe D2D communication signal being properly received. In other words, itis possible to loosen the constraints (for example, the distancesbetween the base station 200, and the reception side device and thetransmission side device and the distance between the reception sidedevice and the transmission side device) for proper reception of the D2Dcommunication signal.

The preferred embodiments of the present disclosure have been describedabove with reference to the accompanying drawings, whilst the presentdisclosure is not limited to the above examples, of course. A personskilled in the art may find various alterations and modifications withinthe scope of the appended claims, and it should be understood that theywill naturally come under the technical scope of the present disclosure.

For example, the example in which the terminal device decides the D2Dtransmission timing of the own device has been described, but anembodiment of the present disclosure is not limited thereto. Forexample, as described even in the applications, the D2D transmissiontiming of the terminal device may be decided by a device forming a partof the base station. For example, in the described example, theinformation acquisition unit and the transmission timing decision unitincluded in the terminal device may be included in the base station (orthe device forming a part of the base station). The base station maynotify the terminal device of the D2D transmission timing.

Also, the processing steps in a communication control process in thisspecification are not strictly limited to being executed in a timeseries following the sequence described in a flowchart. For example, theprocessing steps in a communication control process may be executed in asequence that differs from a sequence described herein as a flowchart,and furthermore may be executed in parallel.

In addition, it is possible to create a computer program for causinghardware such as a CPU, ROM, and RAM built into a communication controldevice (for example, terminal device) to exhibit functions similar toeach structural element of the foregoing communication control device.It becomes also possible to provide a storage medium which stores thecomputer program.

Additionally, the present technology may also be configured as below.

(1)

A communication control device including:

an acquisition unit configured to acquire a reception timing at which asecond radio communication device receives a downlink signal from a basestation performing radio communication with a first radio communicationdevice or the second radio communication device; and

a decision unit configured to decide a transmission timing at which thesecond radio communication device transmits a signal to the first radiocommunication device through inter-device communication based on thereception timing,

wherein the decided transmission timing is a timing later than a timingat which the second radio communication device transmits an uplinksignal.

(2)

The communication control device according to (1),

wherein the acquisition unit further acquires first timing advanceinformation to decide the timing at which the second radio communicationdevice transmits the uplink signal, and

wherein the decision unit decides the transmission timing based on thereception timing and the first timing advance information.

(3)

The communication control device according to (2), wherein the decidedtransmission timing is a timing earlier than the reception timing.

(4)

The communication control device according to (2) or (3), wherein thedecided transmission timing is a timing later than a timing at which thebase station transmits the downlink signal.

(5)

The communication control device according to (4), wherein the decidedtransmission timing is the timing at which the base station transmitsthe downlink signal.

(6)

The communication control device according to (4) or (5), wherein thetiming at which the base station transmits the downlink signal is atiming earlier than the reception timing by half of a time correspondingto the first timing advance information.

(7)

The communication control device according to (1), wherein the decidedtransmission timing is the reception timing.

(8)

The communication control device according to (2),

wherein the acquisition unit further acquires second timing advanceinformation to decide a timing at which the first radio communicationdevice transmits an uplink signal, and

wherein the decision unit decides the transmission timing based on thereception timing, the first timing advance information, and the secondtiming advance information.

(9)

The communication control device according to (8), wherein the decidedtransmission timing is a timing at which the first radio communicationdevice receives the downlink signal from the base station.

(10)

The communication control device according to (9), wherein the timing atwhich the first radio communication device receives the downlink signalis a timing later than a timing at which the base station transmits thedownlink signal by half of a time corresponding to the second timingadvance information.

(11)

The communication control device according to any one of (1) to (10),

wherein the first radio communication device and the second radiocommunication device are located in a same cell, and

wherein the base station is a base station of the same cell.

(12)

The communication control device according to any one of (1) to (10),

wherein the first radio communication device is located in a first cell,

wherein the second radio communication device is located at a secondcell different from the first cell, and

wherein the base station is a base station of one of the first cell andthe second cell.

(13)

The communication control device according to any one of (1) to (12),wherein the first radio communication device and the second radiocommunication device transmit a signal according to a predeterminedradio communication scheme through the inter-device communication andreceive a signal according to the predetermined radio communicationscheme.

(14)

The communication control device according to (13), wherein thepredetermined radio communication scheme is a radio communication schemeused by the base station to transmit the downlink signal.

(15)

The communication control device according to (14), wherein thepredetermined radio communication scheme is an orthogonal frequencydivision multiplexing scheme.

(16)

The communication control device according to any one of (1) to (15),wherein the communication control device is the second radiocommunication device.

(17)

The communication control device according to any one of (1) to (15),wherein the communication control device is a device forming a part ofthe base station.

(18)

A program causing a computer to function as:

an acquisition unit configured to acquire a reception timing at which asecond radio communication device receives a downlink signal from a basestation performing radio communication with a first radio communicationdevice or the second radio communication device; and

a decision unit configured to decide a transmission timing at which thesecond radio communication device transmits a signal to the first radiocommunication device through inter-device communication based on thereception timing,

wherein the decided transmission timing is a timing later than a timingat which the second radio communication device transmits an uplinksignal.

(19)

A communication control method including:

acquiring a reception timing at which a second radio communicationdevice receives a downlink signal from a base station performing radiocommunication with a first radio communication device or the secondradio communication device; and

deciding a transmission timing at which the second radio communicationdevice transmits a signal to the first radio communication devicethrough inter-device communication based on the reception timing,

wherein the decided transmission timing is a timing later than a timingat which the second radio communication device transmits an uplinksignal.

REFERENCE SIGNS LIST

-   10 terminal device-   20 base station-   21 cell-   23 macro cell-   25 small cell-   100 terminal device-   110 antenna unit-   120 radio communication unit-   130 storage unit-   140 control unit-   141 information acquisition unit-   143 transmission timing decision unit-   200 base station

1. (canceled)
 2. An electronic device comprising: circuitry configuredto: obtain receiving timing information related to a timing at which asecond communication device receive downlink signals from a basestation, the base station communicates with a first communication deviceor the second communication device; and determine a transmitting timingat which the second communication device transmit D2D signals to thefirst communication device based on a predetermined condition; whereinthe transmitting timing is determined based on the receiving timinginformation and a first timing advance information corresponding to thesecond communication device in case of a first case according to thepredetermined condition, and the transmitting timing is determined basedonly on the receiving timing information in case of a second caseaccording to the predetermined condition.
 3. The electronic device ofclaim 2, wherein, in case of the first case, the transmitting timing isdetermined as prior to a timing indicated by the receiving timinginformation by a value calculated by multiplying the first timingadvance information by a predetermined coefficient.
 4. The electronicdevice of claim 2, wherein, in case of the second case, the transmittingtiming is determined without considering which a duplex communicationscheme is set, FDD scheme or TDD scheme.
 5. The electronic device ofclaim 2, wherein, in case of a third case according to the predeterminedcondition, the transmitting timing is determined based on the receivingtiming information, the first timing advance information and a secondtiming advance information different from the first timing advanceinformation.
 6. The electronic device of claim 2, wherein thepredetermined condition corresponds to a condition related to positionsof the first communication device or the second communication device. 7.The electronic device of claim 2, wherein the predetermined conditioncorresponds to a condition related to whether the first communicationdevice and the second communication device are located in a same cell ornot.
 8. The electronic device of claim 7, wherein the circuitry isconfigured to obtain the receiving timing information from a basestation different from a base station providing a cell which the secondcommunication device belongs to.
 9. The electronic device of claim 2,wherein the predetermined condition corresponds to a condition relatedto whether the first communication device and the second communicationdevice belong to a same timing advance group or not.
 10. The electronicdevice of claim 2, wherein the transmitting timing is determined as atiming later than a timing at which the second communication devicetransmits an uplink signal.
 11. The electronic device of claim 10,wherein the timing is further later than a timing at which the basestation transmits the downlink signal.
 12. Wireless communication methodcomprising: obtaining receiving timing information related to a timingat which a second communication device receive downlink signals from abase station, the base station communicates with a first communicationdevice or the second communication device; and determining atransmitting timing at which the second communication device transmitD2D signals to the first communication device based on a predeterminedcondition; wherein the transmitting timing is determined based on thereceiving timing information and a first timing advance informationcorresponding to the second communication device in case of a first caseaccording to the predetermined condition, and the transmitting timing isdetermined based only on the receiving timing information in case of asecond case according to the predetermined condition.